1. Field of the Invention
This invention relates generally to rolling mills, and is concerned in particular with an improvement in the finishing blocks of high speed rod rolling mills.
2. Description of the Prior Art
Referring initially to FIG. 1, a conventional high speed finishing block 10 is shown positioned on a mill pass line PL. Product PR is received at the low speed entry end E of the block and exits from the block at the high speed delivery end D. The block is powered from the delivery end via a gear-type speed increaser 12 and a drive motor 14.
The block includes a succession of roll stands 16a-16h alternately staggered on opposite sides of the mill pass line PL. The roll stands have cantilevered pairs of work rolls 18 alternately offset by 90xc2x0 in order to effect twist free rolling of products. The successive roll stands on each side of the pass line are mechanically coupled one to the other and to the speed increaser 12 by parallel line shafts comprising coaxial line shaft segments 20 interconnected by gear-type couplings 22.
The successive roll stands 16a-16h are connected to respective line shaft segment 20 by bevel gears sets 24a-24h. A shown by the plot line xe2x80x9cxxe2x80x9d in FIG. 2, the gear ratios of the successive bevel gear sets are designed to provide stepped increases in their pitch line velocities. The stepped increases are selected to keep pace with the progressively increasing speed of the product being rolled through the block. With this arrangement, the maximum attainable operating speed of the block is limited by the maximum pitch line velocity that can be designed into the bevel gear set of the last operating stand in the block, which in this case is the bevel gear set 24h of the stand 16h.
Thus, for example, if the block is rolling a 7 mm round out of stand 16h at a rate of 120 to 130 tons per hour, and if the last two stands 16g and 16h are then xe2x80x9cdummiedxe2x80x9d by removing their respective work rolls 18 in order to roll a larger 9 mm round out of stand 16f, the maximum obtainable tonnage rate remains the same because the bevel gear sets of the dummied stands remain connected to the mill drive. Moreover, although the dummied stands 16g and 16h are now unloaded, since they continue to be driven off of the line shafts, their bearings, seals, etc. continue to wear.
There exists a need, therefore, for an improved finishing block in which roll stands can be selectively dummied to progressively increase product size, with the dummied stands being completely uncoupled from the mill drive, and with the mill drive arranged such that rolling speeds can be increased progressively to increase the tonnage rate of the larger products being rolled.
A finishing block capable of achieving these objectives in accordance with the present invention will now be described with reference to the accompanying drawings, wherein: